My understanding is that during the later years of Castellano's reign, most family business was run by a 4-man panel of Thomas Gambino, Daniel Marino, Jmmy Brown Failla, and Thomas Bilotti.

Bilotti may not have been particularly clever, but the other three were

Moreover, Castellano supposedly made it known that he wanted Tommy Gambino to be his successor

Therefore, even though Bilotti was promoted to Underboss, it was never the plan to make him boss

A few questions spring to mind:

(1) If the rank-and-file thought that Castellano had gotten his position only through nepotism, would not the same resentment have existed against Tommy Gambino? And yet Tommy Gambino seems to have been a very popular and therefore powerful figure

(2) Even if Castellano were out-of-touch with the street, and supposedly unaware of Gotti's machinations against him, would not such street-savvy figures as Marino and Failla have known the danger?

(3) The hypocrisy of the Gotti accusing the Castellano faction of nepotism, and then making and promoting John Jr at such a young age, and seeing to it that John Jr and Peter Gotti ruled the family after his imprisonment . . . .